In video gaming machines, it is necessary to display many kinds of characters or patterns on a screen and to move, rotate, modify, enlarge or reduce these characters or patterns on the basis of a predetermined program and rule for a game, thereby to develop the required process of the game.
One well-known method of generating those patterns is to use a parallel raster scanning method which is similar to the case of a standard TV receiver, and the other one is a random scanning or vector generating method.
In the former method, each scan line is divided into a number of picture display elements and the luminance of each picture element is controlled; as a result, a picture is displayed as a mosaic pattern consisting of a series of picture elements along the scan line.
With this method, therefore, colorful patterns suitable for a gaming machine can be easily constituted since these patterns are displayed as a combination of various color images. However, in this method, although the generated patterns can be easily moved horizontally and vertically on the screen, there is the problem that a high-speed processing unit and a relatively large capacity memory are needed to rotate, enlarge or reduce these patterns.
Even in the case of an extremely simple pattern, e.g. a square and the like, if one desires to smoothly rotate this pattern, a processing unit which is too advanced and expensive to be used in a gaming machine is required. In other words, it is impossible to smoothly perform the rotation, enlargement, reduction, etc. of a complicated pattern at a high speed by a cheap processing circuit which can be adopted for a raster scan gaming machine; therefore, there is a problem in that, for example, the rotational movement has to be represented by an approximate rotational movement based on the discontinuous rotational indication such that the pattern jumps and is displayed at intervals of, say, 30 degrees of rotational angle or the like.
In the latter random scanning method, the X-Y deflection angles of the electron beam are controlled without using any raster, thereby drawing a line image on the screen.
With this method, since a pattern is displayed as an aggregate of a relatively small number of straight lines, i.e. vectors to be displayed on the screen, little computational effort is necessary to rotate, enlarge and reduce the pattern. Thus, the pattern can be smoothly rotated, enlarged and reduced at high speed even by a low-speed processing unit of small capacity. However, displayed patterns are limited to simple line drawings consisting of a relatively small number of straight lines or to a hollow outline drawing without any filled-in color areas; therefore, there is a problem in that the displayed pattern lacks substance and brilliance and that this may diminish interest in the game.
Spiral scanning of a cathode ray tube is old. For example the article Various Characteristics of the Equal Angular Velocity Spiral Scanning Television published in the Journal of the Institute of Television Engineers of Japan, Vo. 32, no. 9 (1978) teaches a television having spiral scanning.